van der Waals equation

An equation that relates the pressure, volume, and absolute temperature of a gas taking into account the finite size of molecules, and their intermolecular attraction, having the form RT = (P + av-2)(v - b), where R is the gas constant, T is the absolute temperature, P is the pressure, v is the volume of fluid per molecule, a is a measure of the attraction of the molecules for each other (due to van der Waals forces), and b is the volume occupied by a single molecule. The equation accurately captures phase transitions between liquid and gas phases of substances. See also ideal gas law.